Technical Articles
Technical Bulletin: Cyanuric Acid - Chlorine's Stabilizer
It’s a hot, sunny day. The sun is so bright that stepping outside is a reminder to put on sunscreen. Only seconds tick away before the first bead of sweat runs down your forehead. It’s the kind of day that lures people into the nearest pool. It is days like this when cyanuric acid is a superhero, protector of the weak.
How Cyanuric Acid Works
Sunlight and its UV radiation can destroy sanitizer in a very short time. Sanitizers act as the pool police, killing unwanted invaders like bacteria and algae in the water, yet they too have weaknesses. The more intense the sun and UV, the quicker the sanitizer degrades, the pool police can’t work well. Chlorine is the most commonly used sanitizer. On a bright sunny day, nearly all of an ideal level of chlorine in an unstabilized (unprotected) pool can be lost in less than two hours. However, chlorine has an advantage, it can be protected from the sun. Cyanuric acid is used as a “stabilizer” for chlorine so that it is more enduring when exposed to the ultraviolet rays of the sun. It is like sunscreen for your chlorine. Cyanuric acid combines with chlorine to protect it from the UV rays of the sun, but releases it on demand when it is needed to sanitize the water. Cyanuric acid, Triazine-2,4,6-Triol in scientific terms, is an acid with a pH of approximately 4.0. Therefore, cyanuric acid may also shift the pH of the water downward when added directly to a pool.
Why is it important to monitor cyanuric acid levels?
If cyanuric acid is present in the water in sufficient levels, less chlorine degradation occurs. Keeping chlorine in the water longer will help to protect the swimmers in the pool. An ideal level of cyanuric acid, 30 to 50 ppm (parts per million), should be maintained to prevent rapid chlorine loss. Some chlorine compounds have been developed that already contain an amount of cyanuric acid. If you are using “dichlor” or “trichlor” as the primary sanitizer, cyanuric acid is being introduced along with the chlorine. Usually, no additional cyanuric acid is needed when using a stabilized chlorine compound. However, cyanuric acid levels may build up with the continued use of one of these sanitizers. When cyanuric acid levels are high, it will reduce chlorine efficiency, and contribute to high total dissolved solids. Under these conditions it may take chlorine longer to kill bacteria and other microorganisms introduced to the water. If cyanuric acid is high, it is necessary to drain and refill with fresh water in order to lower the level. Local health authorities often require swimming pools to be maintained under 100 ppm. Cyanuric acid levels in pools should not exceed 150 ppm. On the other hand, low cyanuric acid levels (less than 30 ppm) indicate that chlorine will dissipate very quickly when exposed to sunlight.
Testing Cyanuric Acid:
When you add fresh water, you should test the cyanuric acid level until the water is properly balanced. You should then test the cyanuric acid at least monthly throughout the season. If using “dichlor” or “trichlor”, you may need to test cyanuric acid more frequently to ensure that the level has not exceeded the upper limit since both contain cyanuric acid in the formulation. Each time you add a dose of one of these stabilized chlorine compounds, the level of cyanuric acid increases slightly.
There are two methods for testing cyanuric acid that are common to the pool and spa industry.
Test Strip
A test strip is available from AquaChekTM to measure cyanuric acid. A patented chemistry allows for the direct measurement of cyanuric acid using a color reaction proportional to the concentration. This color reaction takes place on the test pad that is compared to a color chart to analyze the level present. A recent improvement in the chemistry allows users to measure up to 300 ppm directly (without the need to dilute a pool water sample). In addition, greater color distinction allows for greater accuracy and ease of use. This is a dip-and-read test that is completed in 30 seconds. Cyanuric acid is also measured by AquaChek Silver, a six way test measuring: free and total chlorine, pH, total alkalinity, hardness and cyanuric acid.
Turbidity Test
The second type of test common to the industry is a turbidity test, often referred to as a “disappearing dot” test. This test utilizes a chemical reaction that creates turbidity proportional to the concentration of cyanuric acid. The more turbid the water, the higher the concentration of cyanuric acid. This turbid water is added one drop at a time to a comparator with a mark (usually a dot) on the bottom. A user adds drops until the mark disappears from view. The turbidity of the water dictates the amount that will be necessary to make the mark disappear. The amount of water in the comparator tube when the mark disappears corresponds to a value marked on the tube to indicate the cyanuric acid level.
The turbidity test can only measure cyanuric acid in a concentration up to 100 ppm. If the level measures 100 ppm or greater, you have to dilute the water to determine how much higher the actual level is. To do this, add fresh water to the sample and run the test over. (For example, let's say that you start with one cup of pool water and one cup of fresh or distilled water. If the turbidity test measures 80 ppm in the diluted sample, that means that the cynauric acid in the undiluted water must be 160 ppm.)
It is important to understand the role cyanuric acid plays in the pool. Test routinely to ensure that an ideal cyanuric acid level is present to give confidence to the user that chlorine is operating under optimal conditions. Compare testing devices to determine which method is best for you.
© 2001
For information or a copy of this technical report call toll free 888-AQUACHEK (1-888-278-2243), or at 219-262-2060.
